Final answer:
A doubly fed induction generator is a type of efficient electric generator where both the stator and rotor are connected to the electrical grid, with the rotor having a variable frequency. It is commonly used in wind turbines to variably control speed and efficiently capture wind energy. The emf produced by a DFIG is a function of its coil rotation speed and the strength of the magnetic field.
Step-by-step explanation:
Doubly Fed Induction Generator
A doubly fed induction generator (DFIG) is a specialized type of induction generator commonly used in wind turbines. It is known for its ability to control the power factor and variably control its rotational speed. In a DFIG, there are two sets of windings: the stator and the rotor, both of which are connected to the electrical grid. The stator operates at grid frequency, while the rotor is fed with an alternating current (AC) with a variable frequency through slip rings or brushes. This allows the rotor speed to differ from the synchronous speed of the grid, making the DFIG more efficient in capturing energy over a range of wind speeds.
The basic principle of a DFIG is similar to that of any electric generator: a coil is rotated within a magnetic field to induce an electromotive force (emf). This is a direct application of electromagnetic induction, where the EMF induced in the generator coil is a function of the rotational speed and the magnetic field. The formula for emf in a rotating coil is given by emf = NABw, where N is the number of turns, A is the coil area, B is the magnetic flux density, and w is the angular velocity.
DFIGs are particularly valuable for their efficiency and the control they offer over the generation process, making them ideal for variable-speed applications like wind turbines. The peak emf that can be generated is a product of the physical characteristics of the generator and its operational speed.